From patchwork Thu Jul 1 08:38:43 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marco Elver X-Patchwork-Id: 12353711 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CDE0BC11F67 for ; Thu, 1 Jul 2021 08:40:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B3126613F1 for ; Thu, 1 Jul 2021 08:40:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235479AbhGAInW (ORCPT ); Thu, 1 Jul 2021 04:43:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40258 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235356AbhGAInV (ORCPT ); Thu, 1 Jul 2021 04:43:21 -0400 Received: from mail-qk1-x74a.google.com (mail-qk1-x74a.google.com [IPv6:2607:f8b0:4864:20::74a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D109DC0617A8 for ; Thu, 1 Jul 2021 01:40:51 -0700 (PDT) Received: by mail-qk1-x74a.google.com with SMTP id e9-20020a05620a12c9b02903b429a77b4cso3105335qkl.5 for ; Thu, 01 Jul 2021 01:40:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:message-id:mime-version:subject:from:to:cc; bh=5iHoNZMOeP6TxsWwP/0krCRRwCbLGs4FQeU+EZRnVpw=; b=FMpj5JxuvGNfBzF6vXgu2ty+hfpspeI/EDm3LJYTsJoaCNE3k6TVARsbPBxXFX4nWm 1HoNvamktFRK3begTvvzpfatrEad5S90Acr/VAL1gvywFra+8hYcXivsK0/KDNEQmoL+ Vfqp6Ej0zCR4SHWdJKdm0irz/YBGo4kKOJyhXv7XrFMuCtX7xJfrRIGY7RGmQMtl2ifu dm8fMDH76QKCAL5NJBWJXdxOoqNHMBdk5/w03UE3OnrblaMwURXPUro8tyjfXesNsIeB tJIHFJqgIgZzyVsNbxUVFSlBS3fFw7lBxxoX5x3NbOv5OZ4Xm2qPiN7EUtBzyqiN9TXX oSVA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=5iHoNZMOeP6TxsWwP/0krCRRwCbLGs4FQeU+EZRnVpw=; b=TFb2en+80ro3UJeuUdQv8LmOHyyNE9CY6P85Xne2s/ZJyOgTBRLKegGHT8YCVYCoTk 9H8FHi/1De3dvH9vGeRCBluYThRCNX62Ucg6/GpYhWsrYIfWdrwh1HYwQu3U9OdzmRMn 2eqoY/nm8e1ckjVCYzUb+fuTMg8CM7b6Z8jSJdHY2rtyTWYnwWwl5I6CLAOilW1mN2yv RmYW7A+9hIsFHd30jJGejjkIwP9aJhPU3vh6nqBzj9vorqMnvzB6FCjE6xTj/Hz3zhPJ 7toFHUJXFN0upfsWHTFJM4xIFQAzMN8SOytNPCIrG6g5DLDx4jVpuu6ksy59VnNXVlBA BfsA== X-Gm-Message-State: AOAM531ug65vbq7BBosy4GYlvFXQbwl/Ha288/Ek0J+Vl+/NeUb9+410 u7Qc6L9u7Zllb5f/yWomxyAPisjP9Q== X-Google-Smtp-Source: ABdhPJzh0BWd6kKdTshLd8GOa6BvrBKw2SUY1e5kpAyenT4O3KV55wn97GNSQeSm1oacAHDSzUhCAtKGzg== X-Received: from elver.muc.corp.google.com ([2a00:79e0:15:13:8b0e:c57f:ff29:7e4]) (user=elver job=sendgmr) by 2002:ad4:4ba4:: with SMTP id i4mr34049163qvw.42.1625128850422; Thu, 01 Jul 2021 01:40:50 -0700 (PDT) Date: Thu, 1 Jul 2021 10:38:43 +0200 Message-Id: <20210701083842.580466-1-elver@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.32.0.93.g670b81a890-goog Subject: [PATCH v2] perf: Require CAP_KILL if sigtrap is requested From: Marco Elver To: elver@google.com, peterz@infradead.org Cc: tglx@linutronix.de, mingo@kernel.org, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, mingo@redhat.com, acme@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, linux-perf-users@vger.kernel.org, ebiederm@xmission.com, omosnace@redhat.com, serge@hallyn.com, linux-security-module@vger.kernel.org, stable@vger.kernel.org, Dmitry Vyukov Precedence: bulk List-ID: If perf_event_open() is called with another task as target and perf_event_attr::sigtrap is set, and the target task's user does not match the calling user, also require the CAP_KILL capability. Otherwise, with the CAP_PERFMON capability alone it would be possible for a user to send SIGTRAP signals via perf events to another user's tasks. This could potentially result in those tasks being terminated if they cannot handle SIGTRAP signals. Note: The check complements the existing capability check, but is not supposed to supersede the ptrace_may_access() check. At a high level we now have: capable of CAP_PERFMON and (CAP_KILL if sigtrap) OR ptrace_may_access() // also checks for same thread-group and uid Fixes: 97ba62b27867 ("perf: Add support for SIGTRAP on perf events") Cc: # 5.13+ Reported-by: Dmitry Vyukov Signed-off-by: Marco Elver --- v2: * Drop kill_capable() and just check CAP_KILL (reported by Ondrej Mosnacek). * Use ns_capable(__task_cred(task)->user_ns, CAP_KILL) to check for capability in target task's ns (reported by Ondrej Mosnacek). --- kernel/events/core.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index fe88d6eea3c2..43c99695dc3f 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -12152,10 +12152,23 @@ SYSCALL_DEFINE5(perf_event_open, } if (task) { + bool is_capable; + err = down_read_interruptible(&task->signal->exec_update_lock); if (err) goto err_file; + is_capable = perfmon_capable(); + if (attr.sigtrap) { + /* + * perf_event_attr::sigtrap sends signals to the other + * task. Require the current task to have CAP_KILL. + */ + rcu_read_lock(); + is_capable &= ns_capable(__task_cred(task)->user_ns, CAP_KILL); + rcu_read_unlock(); + } + /* * Preserve ptrace permission check for backwards compatibility. * @@ -12165,7 +12178,7 @@ SYSCALL_DEFINE5(perf_event_open, * perf_event_exit_task() that could imply). */ err = -EACCES; - if (!perfmon_capable() && !ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) + if (!is_capable && !ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) goto err_cred; }